The present invention relates to a heavy duty rectifier which includes rows of rectifier valves secured to a rectifier bar cooled by forced circulation with the valves of a respective row being electrically connected to a respective connecting bar.
In such known heavy duty rectifiers, on one broadside of the rectifier bar are disposed rows of rectifier valves secured in an electrically conducting manner at roughly the same mutual spacing. Each valve is also electrically connected to a connecting bar through which current is supplied to the valves, there being a connecting bar provided for each row of valves. In one heavy duty rectifier, two rows of rectifier valves are provided and two connecting bars in strip form of roughly equal width are provided, each connecting bar being associated with and through which current is supplied to one row of rectifier valves. Mutually spaced terminals are provided on the connecting bars to which a respective rectifier valve is electrically connected. The mutual spacing of the terminals is approximately the same as that of the associated rectifier valves. Both connecting bars are arranged so as to be spaced from each other, with the side on which the terminals are provided being at an angle to the broadside of the rectifier bar being cooled by forced circulation, and to which are secured the rectifier valves.
Such heavy duty rectifiers with a multiplicity of rectifier valves connected in parallel having at least the bar on which are secured the rectifier valves cooled by forced circulation, are commercially available. It is essential in such heavy duty rectifiers that the load on all rectifier valves be as uniform as possible. This uniformity of load on the individual rectifier valves is associated with a uniform current distribution over the entire length of the bars. In the article "Large Numbers of Parallel Connections in Large Silicon Rectifiers" at pages 544 to 549 of the Siemens-Zeitschrift 42 (1968), it is pointed out that the current distribution in the bars depends on the series and shunt inductances of the system in addition to the distribution of the conduction characteristics of the rectifier valves connected in parallel. Series inductance is understood to be the inductance occurring between two adjacent rectifier valves mounted on the rectifier bar. Shunt inductance is the inductance between each rectifier valve and the associated terminal on the connecting bar. The article teaches that an approximately uniform current distribution is obtained when the series to shunt inductance ratio is as small as possible, assuming the series inductance between any two adjacent rectifier valves corresponds to a mean series inductance. Measurements taken on commercial heavy duty rectifiers show that, despite the observance of this requirement, great variations of up to 50% from the mean value occur in the current distribution along the bars.